The present invention generally relates to backlight devices, and, more particularly, to a backlight device that has a heat-generating light source such as a fluorescent tube.
Conventional display devices normally include CRTs (cathode-ray tubes), but, these CRT displays are being rapidly replaced by flat panel displays that employ liquid crystal panels. These liquid crystal displays have higher display quality today, and therefore are expected to become larger in size and have a higher luminance for use in television sets. Accordingly, backlight devices for illuminating the liquid crystal panels are also expected to have higher luminance.
Conventional liquid crystal displays are used mainly for notebook type personal computers, land the screen size is normally limited to 13 inches. The resolution is XGA at the highest, and the display luminance is only as high as 150 cd/m2. FIGS. 1A, 1B, and 2 illustrate a liquid crystal display 1A of this type.
The liquid crystal display 1A includes a liquid crystal panel 2A, a housing 5, and a backlight device 10A. The housing 5 holds the liquid crystal panel 2A and the backlight device 10A with a resin frame 6 and a backboard 9. The backlight device 10A illuminates the liquid crystal panel 2A from the back, and gives a predetermined luminance to the display screen of the liquid crystal panel 2A.
The backlight device 10A includes a fluorescent tube 3 that serves as a light source, a rubber holder 12 (shown in FIG. 5) that holds the fluorescent tube 3, and a light guide plate 4 that guides the light from the fluorescent tube 3 to the liquid crystal panel 2A. The fluorescent tube 3 contains Ar gas or Ne gas in which mercury is sealed, and the tube wall of the fluorescent tube 3 is coated with a fluorescent material. The mercury gas radiates ultraviolet rays during electric discharge, and the ultraviolet rays then strike the fluorescent material to generate visible rays.
The light guide plate 4 is an acrylic resin plate that cooperates with a provided optical sheet 8 to illuminate the entire area of the liquid crystal panel 2A with the light guided from the fluorescent tube 3. In the liquid crystal display 1A that has a small screen size (approximately 13 inches, as shown in FIG. 1A) and is not required to have a high resolution and a high screen luminance, the backlight device 10A is provided only by one side of the light guide plate 4, and only the single fluorescent tube 3 is employed.
On the other hand, a liquid crystal display 1B for monitoring, which is shown in FIGS. 3A through 5C, normally has a display size of 15 inches, and is required to have a SXGA resolution and a screen luminance of approximately 250 cd/m2. For this reason, two backlight devices 10B are incorporated into the liquid crystal display 1B, with the light guide plate 4 being interposed in between. Further, two fluorescent tubes 3 are provided for each of the backlight devices 10B. As DVD drives for personal computers have been widely spread, however, liquid crystal displays for monitoring are expected to have a larger and brighter screen, so that users can enjoy movies on the screen of the liquid crystal display.
The problem with the liquid crystal display 1B is that the fluorescent tubes 3 provided for each of the backlight devices 10B generate heat as well as light. A temperature rise in the vicinity of the fluorescent tube electrode 11 of each of the fluorescent tubes 3 is particularly large. When the supply current is increased to obtain a higher luminance, the temperature becomes as high as 120xc2x0 C. or even higher. The fluorescent tube electrodes 11 are located at both ends of each of the fluorescent tubes 3. To accommodate each fluorescent tube electrode 11, a heat-conductive rubber holder 12 is provided at both ends of each of the fluorescent tubes 3. Each rubber holder 12 is engaged with the corresponding holder 7, so that both ends of each of the fluorescent tubes 3, where the temperature rises by the greatest degree, can be cooled down.
The rubber holders 12 are situated near the light guide plate 4, and directly face the light guide plate 4. Because of this arrangement, the heat generated by each fluorescent tube electrode 11 is transferred to the light guide plate 4 via the corresponding rubber holder 12.
Due to the heat generated by the fluorescent tube electrodes 11, there is always a risk of melting the part (indicated by the arrow B in FIG. 5C) of the resin light guide plate 4, which faces the fluorescent tube electrodes 11 in each of the conventional backlight devices 10B. When melted in this manner, the light guide plate 4 is deformed and deteriorates. A deformed light guide plate 4 cannot properly guide the light from the fluorescent tubes 3 to the liquid crystal panel 2B, resulting in decreases in the luminance and resolution of the display screen. If the liquid crystal display 1B becomes larger in size and generates a greater amount of heat from the fluorescent tube electrodes 11, this problem will be aggravated even further.
A general object of the present invention is to provide backlight devices in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a backlight device that can prevent the light guide plate from melting, even when the temperature rises due to the heat generated by the light source.
The above objects of the present invention are achieved by a backlight device that includes: a light source that emits light when power is supplied to electrodes thereof; a light guide plate for guiding the light emitted from the light source to a liquid crystal panel; and heat release members for releasing heat generated by the electrodes, the heat release members being located at least either at the electrodes of the light source or at the corners of the light guide plate facing the electrodes.
In this backlight device, the heat release members are located at the positions between the light guide plate and the electrodes, where the heat generated by the light source is most likely to build up. To release the heat, the heat release members are placed by the side of each electrode of the light source, or at the corners of the light guide plate facing the electrodes. Alternatively, the heat release members may be placed both by the side of each electrode and at the corners of the light guide plate.
In this structure, the heat generated by the light source can be released through the heat release members placed between the light guide plate and the electrodes. As a result, the light guide plate can be prevented from melting due to heat generation, even when the light source has a higher luminance and a larger amount of heat is generated by the light source. Thus, the deformation and deterioration of the light guide plate can be avoided.
The above objects of the present invention are also achieved by a liquid crystal display that includes: a liquid crystal panel; the backlight device of the present invention; and a light guide plate that is provided at the light-entering surface side of the backlight device, and guides the light emitted from the backlight device to the liquid crystal panel.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.